Status of the η/η’ run (April 2009) A.Starostin UCLA

April’09 run: overall statistics Main run parameters: 10 cm – long LH2 target multiplicity 3+ in CB; threshold in CB 360 MeV two layers of PbOW4 crystals 10mkm Cu radiator; 4 mm collimator Run period: Started: evening April 2nd, 2009; Finished: early morning April 20th Total hours: ~320h. Total runs: ~720 ~660 full target; ~20 empty target; ~40 tagger efficiency Total data: ~1.15 Tb average size 1.69 Gb/file, a typical “good” run is 1.85 Gb: run stability ~91% average data rate ~3.6 Gb/h, typical data rate for a “good” run ~4.1 Gb/h, run efficiency ~87%

Physics statistics: Main physics objective of the run was achieved – about 9500 detected η->3π0 per hour (about 105 η produced per hour) The total statistics for the run is ~3M detected η->3π0, about the same as the summer-fall 2007 run collected in 750 hours The achieved rate is still 1.5-2 times lower compared to the rate in the new 2009 η proposal. The rate above does not include data from the two inner TAPS rings. The rings would add another 10-15% to the statistics. Unfortunately there are serious problems with the detectors.

Two TAPS inner rings: History of events: Substantial decrease in the DAQ life time was observed in the previous runs because of the readout of the two inner rings. Because of that we decided to increase the crystals threshold to cut pedestals out. This was done before the April 09 run. After the first one or two days of running we were advised by the TAPS people that the readout is not correct (ADC mapping mixed up?). The correct map was loaded with high thresholds. This configuration worked well, except that we did not have the pedestals recorded. After another four days of running it was decided to lower the thresholds (assuming a correct ADC map) so we would have the pedestals. We kept this configuration if the lifetime would remain reasonable. Unfortunately something was done wrong.

Problems this the inner ring Unfortunately most of the data were taken with the right figure for the TAPS inner ring (wrong ADC map again?) The effect of this problem on the total data rate is about 20% though the increase of the lifetime (~10%) and descries in the acceptance (~10%)

Summary April 2009 run was in general a success: rate of about 10000 detected η->3π0 per hour was achieved. The MAMI-C total eta statistics was almost doubled. Some problems remain, in particular readout of the TAPS inner ring. This problem maybe not as simple as it looks: ideally we would need a pedestal (low threshold) readout during, for example scaller event, and high threshold for all other events. The rate should be doubled to achieve the rate assumed for the 2009 proposal. Fixing the TAPS inner ring problems and increasing the DAQ speed seem to me as the most desirable ways to increase the rate.